1. Field of the Invention
The present invention relates to an image forming unit for use in an image forming apparatus, and more particularly, to an image forming unit which can be removably attached to an image forming apparatus such as copying machine and printer provided with a photoconductive drum, a cleaning device for the photoconductive drum and the like.
2. Description of Related Art
In recent years, in a small-sized personal type image forming apparatus, an image forming unit which is incorporated with photoconductive drum and other image forming devices such as developing unit, cleaning device and charger is removably used in consideration of reproducing a multi-colored image by one image forming apparatus with simple and convenient maintenance, wherein the image forming unit mounted in the image forming apparatus is abandoned when the developer accommodated in a developing unit is consumed, and a new image forming unit is mounted therein.
In order to cope with such a disposable type image forming unit, the image forming apparatus has to be provided with a spare image forming unit. However, the spare image forming unit is left unused for three months or nearly a year, for instance, when the unit is applied to an image forming apparatus which is not used often. In the conventional spare image forming unit, the blade of a cleaning device comes into continuous contact with the same portion of photoconductive surface of photoconductive drum for over a long period of time, and consequently, creep deformation is produced on that portion thereby losing roundness on the photoconductive surface in the transverse section of the photoconductive drum. The lubricant coated on the blade is stuck to the surface of the photoconductive drum to form a film thereon by which charging capacity of the photoconductive drum on that portion and attenuation characteristic are varied, and the blade is deformed by the pressing contact with the drum in the long period of time.
Published Unexamined Utility Model Application 126251/1984 discloses an image forming unit which is capable of solving the problem, wherein the image forming unit is used for a divisible type image forming apparatus whose main body is divided into upper and lower portions. The blade of a cleaning device which is provided in the image forming unit is connected with a working member which is moved correlatively with opening and closing action of the upper unit relative to the lower unit. The working member presses the blade to come in contact with the photoconductive surface of the photoconductive drum correlatively with closing movement of the upper unit on which the image forming unit is mounted and is also activated to move the blade away from the photoconductive drum correlatively with the opening movement of the upper unit relative to the lower unit.
Accordingly, when the image forming unit is not mounted on the image forming apparatus and when the upper unit is not closed relative to the lower unit, the blade is held in a state away from the photoconductive surface of the photoconductive drum thus solving the problem which is caused by an unused state of the image forming unit over a long period of time. When the image forming unit is mounted on the image forming apparatus and the upper unit is closed, the blade is pressed to come in contact with the photoconductive surface of the photoconductor so that the surface of the drum can be cleaned. Further, the blade is separated from the photoconductive drum when the upper unit is opened relative to the lower unit.
However, in a method of separating the blade of the image forming unit from the photoconductive drum correlatively with the opening and closing movement of the upper unit relative to the lower unit, the working member is only moved for opening and closing action of the upper unit relative to the lower unit and the working member itself is comparatively strongly urged by a spring in order for the blade to properly come into contact with or separate away from the photoconductive drum by the correlative movement, and the working member is connected with the blade by the spring. In a type of apparatus wherein a blade is moved either to the position to come in contact with the photoconductive drum or to the position away from the drum correlatively with the opening and closing movement of the upper unit relative to the lower unit, when the image forming unit is attached or detached for maintenance and the photoconductive drum is attached or detached from the image forming unit, it can protect the photoconductive drum from getting scratched which occurs by contact with the blade when the drum is attached or detached. However, in case of the disposable type image forming unit, the number of labors and parts are wastefully increased to unnecessarily raise the manufacturing cost.